The linguist Benjamin Whorf was one of the first to state that thought is determined by the language we use, and thus different cultures, since they are linguistically different, will think in different ways. For instance, in German there are a number of words for on: an, im, auf, um. A Whorfian linguist would say that Germans make fine distinctions about the placing of objects, but English speakers do not, and therefore we are unable to think about "on" in the same way.

Lila Gleitman, a professor of psychology at the University of Pennsylvania who has been studying linguistics for more than 40 years, ran an experiment using English and Korean words to disprove the Whorfian hypothesis.

She gave children and adults three pictures of a plastic shape being "put on" various other plastic shapes. In two of the three scenes, the Korean word that was applied was "kkita"; in the other it was "nohta". She then asked her subjects to generalise to other scenarios. Almost without exception, everyone could do the task. Kkita can be translated as to "put on" or "put in with a snug fit", nohta was a "loose fit". For example, we know that putting a glove on a hand, or a ring on a finger is noticeably different from putting a suitcase on a table.

However, Gleitman's beliefs were recently challenged by a team of scientists who chose to work with a Mayan tribe, the Tenejapans, who speak Tzeltal. The tribe lives on a steep hill. The top of the hill faces southward, the bottom faces north.

They have no words for left and right, instead they use south and north and a third spatial direction that is roughly a diagonal across the hill. Whereas we would say, "Pass me the spoon that's to the left of your teacup," a Tenejapan would say, "Pass me the spoon that's to the south of your teacup." Here, the Whorfians believed, was the perfect place to show that language influences how you think.

The team laid out a table with toy animals on it - a frog, a fish and an insect. They asked the Tenejapans to memorise the layout of the animals, then turn around to a second table placed behind them and rotated at 180 to the first and set the animals up on this table. Without exception, they laid the frog, which had been facing south, facing south on this new table, and the insect that had been facing north, north. As the Whorfians predicted, they laid the animals out using concepts taken from their use of language.

When the same experiment was carried out in the Netherlands, the Dutch replaced the items relatively or egocentrically. They put down the frog, which had been to their right, on the right again, but now facing south. As Gleitman says: "The overwhelming majority of Tenejapan speakers quite consistently rearranged the animals so that after rotation they were heading in the same cardinal direction, whereas Dutch speakers overwhelmingly rearranged the animals such that if these had been facing left on the first table, they faced left after rotation as well. The difference is that what is north does not vary under rotation, whilst what is left certainly does."

It seemed proof that how we speak does indeed alter how we think about the world. Until, that is, Gleitman noticed where the experiments had been carried out. To keep everyone at their ease, the experiment was done in familiar places for the subjects - outside the meeting house on the hill where the Tenejapans lived, and in a lab for the Dutch. Gleitman devised an alternative experiment.

She followed the same procedure but this time used American students at her university. One group was in a featureless room with the blinds down, like the Dutch in their lab. The other group had the blinds open and could now see across the street to a library - this was like the Mayan group where the subjects could orient themselves within their environment. This latter group also responded like the Mayans, they kept the objects in the same order with reference to their surroundings, whereas those in the featureless room altered the order like the Dutch had done, so that the animal to their left was still on their left when placed on the second table.

Gleitman had shown that environment alters our awareness of space, and language is merely used to describe the situation. In fact, of two Tamil-speaking communities, the more urbanised residents of the city Madurai used egocentric words. The reason, she believes, is because small, rural communities can easily use landmarks, like the Tenejapans and their hill.

"'You'll find the railroad station just north-east of the Drexel university parking lot,' is not too useful a direction to give the British tourist who has just arrived in Philadelphia," says Gleitman. In contrast, turn left at the next set of traffic lights and take the third right, is more helpful to the urbanite.

There is one exception, though. Gleitman is originally from Manhattan, New York. "Culturally diverse - some would even say 'literate' - as this community is, its residents share a small, stable, geographical landscape, rich in mutually known landmarks." Like the Tenejapans, directions are absolute: uptown, downtown and crosstown. She recounts a story of two Swedish tourists who got hopelessly lost at the George Washington bridge faced with two signs for uptown, and one for downtown while they were trying to reach midtown.

"The George Washington bridge is at 175th Street, which is uptown, except if you are way uptown already and then it's downtown," she adds. In the end, as Gleitman says, "It's not the word that matters, it's the thought that counts."